Sound-absorbing polymer foam molded article

ABSTRACT

A polymer foam moulded part is described with an improved sound absorption capacity in the frequency range above 1,500 Hz, in which the improved sound absorption capacity is produced by perforating the surface compacted layer of the moulded part.

[0001] The invention relates to polymer foam moulded parts with improved sound absorption capacity.

[0002] Polymer foam moulded parts, in particular also polyurethane foam moulded parts, are frequently used for insulating equipment housings, especially also in the automotive sector, for example as vehicle boot coverings, longitudinal pillar coverings, etc. In this connection the foam moulded parts are generally produced as a two-dimensional extended sheet with a foam moulded part thickness of 0.5 to 5 cm. The two-dimensional extended sheet may be curved in the third dimension.

[0003] Such foam moulded parts have an external layer that is compacted relative to its volume, this layer also being termed the skin. The compaction of the surface is effected during the production of the moulded foam by contact of the still unhardened foam composition with the mould surface, whereby foam bubbles present on the surface are destroyed. The surface skin is an inherent feature of moulded foam. Attempts by the use of special foaming agents or by chemical modification of the foam-forming composition to reduce the tendency to form a surface skin have been only partially successful.

[0004] In DE-OS 25 25 051 film-foam laminates are described that may consist of an open-cell polyurethane foam and a deformable, perforated film joined to the latter that may for example be a plastics or metal sheet.

[0005] Foam moulded parts are used in the automotive sector and in the equipment insulation sector to absorb sound, especially in the range above 1,000 Hz, in particular above 5,000 Hz.

[0006] It has now been found that the sound absorption in the range of the aforementioned higher frequencies can be improved if the moulded foam skin is perforated.

[0007] The present invention accordingly provides polymer foam moulded parts with improved sound absorption capacity in the frequency range above 1,500 Hz, that are characterised by a perforation of the surface compacted layer.

[0008] Preferably the perforation consists of holes of 0.1 to 10 mm diameter, particularly preferably 0.3 to 3 mm diameter. The perforation according to the invention is however not restricted to holes of circular diameter. Oval or slit-shaped perforations may advantageously be used. Particularly preferred are slit-shaped perforations with a cross-section ratio of 1:5 to 1:100. In the case of slit-shaped perforations these are preferably arranged in at least 2 directions on the surface.

[0009] Furthermore, circular slits in the shape of closed or broken circles are also suitable.

[0010] In the case of non-circular, hole-like perforations the smaller cross-section dimension should preferably be 0.1 to 3 mm, particularly preferably 0.5 to 2 mm.

[0011] The total area of the perforations may account for up to 50% of the compacted surface. In general a total area of the perforations of between 0.1 and 10% of the compacted surface is sufficient. Particularly preferably the total area of the perforations is between 1.5 and 4% of the surface.

[0012] Preferably polyurethane foam moulded parts with a density of 60 to 120 kg/m³ are used. The invention is not however restricted to the preferred moulded foam densities that are normal for terrestrial applications. It is also employed for the much lower densities of down to less than 10 kg/m³ that are normally used in aircraft construction.

[0013] The perforation should obviously not penetrate the moulded foam part itself, but simply the compacted layer of the surface.

[0014] The perforations are advantageously formed at the same time as the normally executed rolling of the polymer foam moulded part in order to increase the open-pore structure of the foam. For this purpose the rollers are preferably provided with needles or cylindrical burls that drill through the compacted surface layer of the polymer foam moulded part during the rolling process. Preferably cylindrical hollow burls are used that are open at their front face and have a cutting surface on their external edge.

[0015] The invention is illustrated hereinafter with the aid of Examples 1 to 3.

EXAMPLES Example 1

[0016] A polyurethane foam moulded part of density 80 kg/m³ and thickness 25 mm is used. Test pieces of 20 mm diameter are cut from the flat, two-dimensional moulded part, perpendicular to the surface of the moulded part. The frequency-dependent sound absorption is measured according to ASTM E 1050-90 in a sound absorption tube of 20 mm diameter. Curve a) of the accompanying FIG. 1 shows the measured sound absorption of the test body with non-perforated surface skin.

Example 2

[0017] The test body produced according to Example 1 is provided on its surface with ca. 1 mm size holes whose total area makes up 1% of the overall surface. The corresponding sound absorption curve is curve b) of FIG. 1.

Example 3

[0018] The test body is prepared corresponding to Example 1, but in this case the total area of the perforations makes up 2% of the surface. The corresponding sound absorption curve is curve c) of FIG. 2. 

1. Polymer foam moulded part with improved sound absorption capacity in the frequency range above 1,500 Hz, characterised by a perforation of the surface compacted layer.
 2. Moulded part according to claim 1, characterised in that the perforation consists of holes of diameter from 0.1 to 10 mm.
 3. Moulded part according to claim 1 or 2, characterised in that the perforation consists of holes of diameter from 0.3 to 3 mm.
 4. Moulded part according to any one of claims 1 to 3, characterised in that the total area of the perforations amounts to between 0.1 and 10% of the surface.
 5. Moulded part according to any one of claims 1 to 4, characterized in that the total area of the perforations amounts to between 1.5 and 4% of the surface.
 6. Moulded part according to any one of claims 1 to 5 of polyurethane foam with a density of 60 to 120 kg/m³. 